Presented by Louis Perkins Cnidaria Presented by Louis Perkins

Facts Contains over 9000 species of animals found exclusively in aquatic environments Some specialists recognize only 3 classes, though 4 are generally accepted: Anthozoa, Cubozoa, Hydrozoa, Scyphozoa

General Characteristics Diploblastic Radial Symmetry No body cavity – Acoelomate Heterotrophic Sexual and asexual reproduction Ectothermic No cephalization Single orifice used for digestion and respiration

Cnidaria have no brains or central nervous systems Have nerve nets consisting of sensory neurons that generate signals in response to various types of stimulus, such as odors, motor neurons telling muscles to contract, and cilia. Connected by intermediate neurons

Cnidocytes All Cnidarians at least one type of cnidocyte (from which the name is derived) Nematocysts – used to capture prey by injecting venom Spirocysts – used to capture prey by entanglement (only Athozoa) Ptychocysts – used to build protective tubes for owners to live (only certain Anthozoans)

Basic Structure Members of Cnidaria exist in two forms: Polyp and Medusa

Many of the Cnidaria can alternate between these two forms

Reproduction Often involves a complex life cycle with both polyp and medusa stages Sperm and ova are ejected into water After fertilization, larvae, called planulae, form Planulae find suitable location and hook themselves to sea floor Either stay as a polp or strobilates to produce multiple medusa forms

All known Cnidaria can reproduce asexually by various means – budding, segmentation, regeneration

Feeding Nematocysts inject poison into prey – triggered by cilium Tentacles and/or cilia move food into gastrovascular cavity through the mouth Nematocysts can continue to fire even when the tentacle is detached

More Feeding Prey includes bacteria, protozoans, zooaplankton, fish, or other aquatic creatures Many species also contain zooxanthellae, photosynthetic protists or zoochlorellae, photosynthetic algae, within body cells Some species absorb organic compounds from the water

Movement Medusae swim by a form of jet propulsion: muscles squeeze water out of cavity Not enough power to swim against currents and just enough to control movement within currents Hydras and some sea anemones can move slowly by creeping like snails, crawling like inchworms or somersaulting. click here

Importance to Humans Jellyfish stings killed about 1,500 people in the 20th century Jellyfish considered delicacies in Asian cultures Coral reefs are economically important as providers of fishing grounds, protectors against currents and tides, and centers of tourism The "sea wasp” Chironex fleckeri has been described as the world’s most venomous animal is held responsible for 67 deaths

Questions

Cnidaria fall under which category of symmetry?

What are the two body types of Cnidaria?

Fire coral fall under which class of Cnidaria?

Which type of cnidocyte contains poison?

Are Cnidarians diploblastic or triploblastic?

True or False: Chironex fleckeri is a species of coral

Thank You!!